A large number of reasons exist for lighting a large underwater environment including security, safety and illumination of work surfaces. Applications include oil drilling platforms, lighting around submarines and ships and for storage pools. In all applications it is desirable to use a high efficiency, long lifetime light source which can provide continuous lighting with minimal maintenance. Nowhere is the need for a low maintenance lighting system more pronounced than in nuclear facilities in spent fuel storage pools and reactor vessels, and in other nuclear environments, in which water is used to slow the reaction rate, where service of the lighting system results in radiation exposure for maintenance personnel.
Typically, these pools require a large number of lights for effective illumination. Traditionally this lighting has been accomplished using 1000 W, 120 V incandescent spotlights or floodlights. These bulbs have lifetime ratings of 2,000 to 4,000 hours, and provide total light output of 17,000 lumens. At a lifetime of 4,000 hours, a particular light fixture will require 2.19 bulb changes per year, with maintenance personnel being exposed to radiation at each bulb change. A typical fuel storage pool uses 50 incandescent light fixtures. Thus, maintenance personnel are subjected to short periods of radiation quite frequently for single bulb changes or to extended periods of exposure for "en mass" changes.
High pressure sodium (HPS) lighting has been used extensively for street and parking area illumination, lighting in factories and for security lighting. The primary advantages of HPS lights are 1) high efficiency and 2) very long lifetime. Compared to an incandescent bulb, an HPS bulb has a lifetime rating of 24,000 hours and provides a total light output of 140,000 lumens. Simple math emphasizes the advantages of HPS lights: one HPS bulb provides the light of eight incandescent bulbs for six to twelve times longer.
It would be desirable to take advantage of the long lifetime of HPS lighting for illumination of hazardous underwater environments.